Fact-Finding Report on Ambient Temperature Adjustment for Raceway and Cable Systems Exposed to Sunlight on Rooftops

Transcription

1 Effectiveness of Circuit Breakers in Mitigating Parallel Arcing Faults in the Home Run UL Corporate Research 333 Pfingsten Road Northbrook, IL USA File IN16969 Project 11CA25532 October 10, 2011 Issue Date: 11 October 2011 Fact-Finding Report on Ambient Temperature Adjustment for Raceway and Cable Systems Exposed to Sunlight on Rooftops Prepared for Travis Lindsay Consulting Services, Inc. Las Vegas, Nevada Report by Paul W. Brazis, Jr., PhD Fan He, PhD Reviewed by Pravinray D. Gandhi Copyright 2011 Underwriters Laboratories Inc. Underwriters Laboratories Inc. authorizes the above named company and the National Fire Protection Association to reproduce this Report provided it is reproduced in its entirety.

2 NOTICE Fact-Finding Investigations are undertaken to develop facts and issue a Report for use by the Client in seeking amendments in nationally recognized installation codes and standards. The issuance of this Report does not constitute an endorsement of any proposed amendment and in no way implies Listing, Classification or other recognition by UL and does not authorize the use of UL Listing or Classification Marks or any other reference to Underwriters Laboratories Inc. on, or in connection with, the product. Underwriters Laboratories Inc., its employees, and its agents shall not be responsible to anyone for the use or nonuse of the information contained in this Report, and shall not incur any obligation or liability for damages, including consequential damages, arising out of or in connection with the use of, or inability to use, the information contained in this Report.

3 EXECUTIVE SUMMARY The 2011 National Electrical Code (NEC ) requires for circular raceways exposed to sunlight on rooftops, an adjustment temperature be added to the outdoor temperature when determining ambient temperature and associated correction factors for calculating the ampacity of conductors. This adjustment temperature adder for circular raceways exposed to sunlight on rooftops is to account for solar heating, and is needed to assure that no conductor is used in a manner such that its operating temperature exceeds that for which it is designed. In preparing for the 2011 NEC, a proposal was submitted to include cables into the scope of this requirement. Although supporting documentation included a report of testing with MC cables, the Code Panel chose to reject this proposal since the term cables was too general, and that testing was insufficient since only MC cable in a single size was tested. Some of the Code Panel members also noted the need for a more comprehensive research project to determine the effects of sunlight on wiring systems in general when installed on rooftops. This is a report of a Fact-Finding Investigation intended to provide technical data and other pertinent facts regarding the safety aspects of installing raceways and cables to direct sunlight on or above rooftops. The investigation included tests on 17 different types and sizes of wiring systems, each of which were installed at four different elevations above the roof at an outdoor test facility in Las Vegas, Nevada. In addition to temperature measurements on the wiring system conductors, outdoor ambient temperature, wind speed, and solar irradiance were also recorded during the summer months of By calculating the difference between the temperature on the wiring system conductors and the outdoor ambient temperature during the period of peak solar irradiance during selected days of full sun and minimum wind, inferences could be made about the effects of solar heating on these wiring systems. A statistical analysis of the data also provided insights into how solar heating affects wiring systems in general when installed on or above a rooftop. For all wiring systems mounted directly on the roof, the maximum temperature rise above outdoor ambient with a 95% confidence interval would statistically be 62.2 o F. For all wiring systems mounted at a distance above the roof (1/2 inch and greater) the maximum temperature rise above outdoor ambient with a 95% confidence interval would statistically be 51.4 o F. page 3

4 TABLE OF CONTENTS Notice... 2 Executive Summary... 3 Table of Contents... 4 General... 5 Objective... 6 Wiring Systems and Rooftops... 7 NEC Requirements... 7 Comprehensive Test Program to Address Wiring Systems Exposed to Sunlight on Rooftops... 9 Test Sample Selecetion... 9 Test Considerations Test Results Data Analysis Summary Appendix A Test Samples Appendix B Test Instrumentation Appendix C Graphs of Daily Outdoor Ambient Temperature, Solar Irradiance, and Wind Speed Appendix D Description of Boxplot Diagrams for Data Analysis page 4

5 GENERAL A proposal was accepted for the 2008 National Electrical Code (NEC ), which recommended that for conduits exposed to sunlight on rooftops, an adjustment temperature be added to the outdoor temperature when determining ambient temperature for the correction factors in Tables and The substantiation for this proposal noted that Section required that no conductor shall be used in such a manner that its operating temperature exceeds that designated for the type of insulated conductor involved. It also cited testing that showed the air inside conduits in direct sunlight to be significantly hotter than the surrounding air. This proposal resulted in new Section (B)(2)(c) and new Table (B)(2)(c) for the 2008 NEC 1. For the 2011 NEC, a similar proposal was submitted to include cables into the scope of this requirement. Although supporting documentation included a report of testing with MC cables, the Code Panel chose to reject this proposal since the term cables was too general, and that testing was insufficient since only MC cable in a single size was tested. Some of the Code Panel members noted the need for a more comprehensive research project to determine the effects of sunlight on conduits, MC cable, and cable in general when installed on rooftops. 1 For the 2011 NEC, Sec became Sec (A)(3), Sec (B)(2)(c) became Sec (B)(3)(c), and Table (B)(2)(c) became Table (B)(3)(c). page 5

6 OBJECTIVE The objective for this Fact-Finding Investigation is to provide technical data and other pertinent facts regarding the safety aspects of installing raceways and cables to direct sunlight on or above rooftops. Travis Lindsey Consulting Services Inc. proposes to submit a public proposal to revise Section (B)(3)(c) of the 2011 NEC as follows: (c) Circular Raceways and Cables Exposed to Sunlight on Rooftops. Where conductors or cables are installed in circular raceways or where in cables exposed to direct sunlight on or above rooftops, the adjustments shown in Table (B)(3)(c) shall be added to the outdoor temperature to determine the applicable ambient temperature for application of the correction factors in Table (B)(2)(a) or (B)(2)(b). Table (B)(3)(c) Ambient Temperature Adjustment for Circular Raceways or Cables Exposed to Sunlight on or Above Rooftops Distance Above Roof to Bottom of Conduit Raceway or Cable 0-13 mm (1/2 in.) Above 13 mm (1/2 in.) - 90 mm (3-1/2) in.) Above 90 mm (3-1/2 in.) mm (12 in.) Above 300 mm (12 in.) mm (36 in.) o C Temperature Adder o F page 6

7 WIRING SYSTEMS AND ROOFTOPS NEC Requirements Wiring methods and materials are described in Chapter 3 of the NEC. Included in Chapter 3 are various Articles for different cable types and raceways for containing conductors for general wiring, including wiring that may be installed on a rooftop and exposed to sunlight. Although the uses permitted for these various cables and raceways do not specifically mention rooftops, it could be assumed that if permitted for outdoor use and/or wet locations, and resistant to sunlight, a particular wiring system could be installed on a rooftop exposed to sunlight. Tables 1 and 2 include the various cable and raceway systems from Chapter 3 that could typically be installed on or above rooftops exposed to sunlight as permitted by the NEC. Also included in these tables are the specific NEC Chapter 3 Article, the UL standard, and the range of sizes that would be permitted or could be listed. page 7

8 Table 1 Cables Suitable for Installation on Rooftops Exposed to Sunlight Wire Size Type NEC Article UL Standard Min Max Comment MV If identified for use in direct sunlight, or as "MV or MC" MC MI Max 4 AWG for 2 & 3 conductor; 6 AWG for 4 conductor; 10 AWG for a 7 conductor UF /0 For use with PV (rooftop) systems; Max 6 AWG for multiple conductors. This can also include single conductor cable listed as PV wire. TC When marked "Sunlight Resistant" SE unspecified Table 2 Conduits and Raceways Suitable for Installation on Rooftops Exposed to Sunlight Trade Size Type NEC Article UL Standard Min Max Comment IMC /2 4 RMC 344 6/6A 3/8 6 LFMC /8 4 PVC /2 6 LFNC /8 4 When listed as suitable for outdoors EMT /797A 1/2 4 Auxiliary Gutters When listed for exposure to sunlight and wet locations Cable Bus 370 When identified for outdoor use Metal Wireways When listed for wet locations Nonmetallic Wireways /5A When listed for wet locations page 8

9 COMPREHENSIVE TEST PROGRAM TO ADDRESS WIRING SYSTEMS EXPOSED TO SUNLIGHT ON ROOFTOPS Test Sample Selection Various test samples were chosen because of their expected use on rooftops exposed to sunlight, and their similarity to other raceway and cable systems that were not tested, but considered to be representative of these other wiring systems for test purposes. For cables, Type MC cable was chosen to represent metal clad and metal sheathed cables and conduits (e.g. Type MC, MI, LFMC, etc.). Sizes 12 AWG, 1/0 AWG, and 500 kcmil were chosen to represent cables of the smaller, medium, and larger sizes. Type SE and TC cable was also chosen in the 1/0 AWG size to represent jacketed cables (e.g. Type SE, TC, MV, UF, etc.) For conduits and tubings, Type RMC and EMT were chosen to represent circular metal raceways (e.g. RMC, IMC, EMT, etc.). To represent the smaller sizes, trade size ½ was chosen for RMC, and trade size ¾ was chosen for EMT. For the medium and larger sizes, trade sizes 1-1/2 and 4 respectively were chosen. Type PVC was chosen to represent nonmetallic conduits and raceways. To represent the smaller sizes, trade size ¾ was chosen, and for the medium and larger sizes, trade sizes 1-1/2 and 4 respectively were chosen. For other metal wiring systems (e.g. metal wireways, gutters, etc.), metal raceway was chosen in the 4x4 inch and 8x8 inch sizes to represent smaller and larger raceways in general. Table 3 is a summary of the proposed testing to consider a comprehensive research program to determine the effects of direct sunlight when conduit, MC cable, and wiring systems in general are installed on or above a rooftop. page 9

10 Table 3 Summary of Test Samples Raceway/ Cable Type Conductor Size* Trade Size Installed Conductor Size* Number of Conductors MC 12 3 MC 1/0 3 MC SE 1/0 3 TC 1/0 3 RMC 1/ RMC 1-1/2 1/0 4 RMC PVC 3/ PVC 1-1/2 1/0 3 PVC EMT 3/ EMT 1-1/2 1/0 5 EMT Metal Raceway 4x4 in. 1/0 3 Metal Raceway 8x8 in * - AWG or kcmil (copper), Type THHN/THWN. Test Considerations Laboratory Site The testing was conducted at an outdoor laboratory site located in Las Vegas, Nevada. This area was chosen for its broad range of days with higher solar radiation intensity. Fig. 1 Las Vegas, Nevada Outdoor Test Site page 10

11 Roof - To support Table (B)(3)(c) from the 2011 NEC, each wiring system was tested directly on the roof, and at distances of 1/2, 3-1/2, and 12 inches above the roof 2. For wiring systems tested directly on the roof and at 1/2 inch above the roof, the roof was asphalt painted black in color to account for additional heating from solar absorption on the roof. For wiring systems tested at distances greater than 1/2 inch above the roof, the roof surface was asphalt painted white in color to account for additional heating from solar reflection from the roof. Each roof structure was flat, approximately five feet off the ground, and measured 13-1/2 by 10 feet, with R19 fiberglass batt insulation under the roof deck. Fig. 2 Samples Mounted Directly on Black Roof Fig. 3 Samples Mounted 12 Inches off White Roof Test Samples Each test sample was 10 feet long exposed along the horizontal length of the roof surface. A thermocouple was secured to each conductor insulation midway along the length of the sample. The thermocouples were type T, No. 24 AWG, with welded junctions. For the Type MC cable samples, the thermocouple was secured near the conductor. For samples with more than three conductors, a maximum of three thermocouples were used. See Appendix A for a thorough description of each test sample. The ends of each wiring system were closed with surgical cotton to restrict air flow. The wires were not energized during the testing since the object of the testing was to obtain a measurement of the wiring system temperature increase due to the influence of exposure to the sun. 2 Although the breakpoints in Table (B)(3)(c) are for distances of above (greater than) ½, 3-1/2, and 12 inches above the roof, the test samples were located at these breakpoint distances to represent a worst-case test condition. page 11

12 Fig. 4 Thermocouples Installed on Conductors Fig. 5 Cotton Used to Close Ends of Wireways Data Measurements - Temperatures were measured at 1 minute increments throughout the day, and the maximum of the 1 minute increments for a 5 minute time period was recorded. This resulted in 12 recorded measurements per hour. In addition to the measurement of temperature of the conductor insulation of each test sample, the near-by outdoor air temperature was measured in two aspirated enclosures located approximately 8 feet and 13 feet above grade level in the vicinity of the roofs and test samples. Wind speed was similarly measured in the same vicinity using two anemometers. Solar irradiance was measured using a pyranometer located in the same plane as the roof surface. Fig. 6 Aspirated Enclosure for Outdoor Temperature Fig. 7 Anemometer for Wind Speed Measurement page 12

13 Solar irradiance and wind speed was recorded along with the test sample temperatures. Measurements were recorded during the months of June, July and August of Sufficient data was recorded to enable supportable and statistical inferences regarding expected ambient temperatures for raceway and cable systems exposed to sunlight on rooftops. Solar Irradiance - Solar irradiance, or radiation from the sun, is measured as power density in Watts per square meter (W/m 2 ). This solar radiation reaching the earth can vary depending on several factors, including as time-of-day, time-of-year, atmospheric conditions such as clouds, haze, rain, etc., as well as geographical location. The maximum solar radiation reaching the earth s atmosphere can approach 1400 W/m 2, however, W/m 2 is more typical of maximum surface irradiance on a sunny day in many parts of the United States, and can be less during the winter, and much less on cloudy days. Solar photovoltaic (PV) modules are tested and rated under what is referred to as standard test conditions, or STC for short. These standard test conditions are solar irradiance of 1000 W/m 2 and air temperature of 25 o C. 3 In the NEC, PV system components, such as wire size and overcurrent protection, are based on these standard test conditions, with adjustment factors for periods of time where the maximum solar irradiance can exceed 1000 W/m 2. 4 Figure 8 shows a graph of the solar irradiance at the test site incident to the test roofs on June 22, The day was full sun, maximum outdoor ambient temperature of 110 o F, and near the time of summer solstice. The solar irradiance that day exceeded 1000 W/m 2 for a three-hour period beginning at 11:10 am. The NEC defines in Article 100 a continuous load as a load where the maximum current is expected to continue for 3 hours or more. 3 Underwriters Laboratories Inc., UL Standard for Safety for Flat-Plate Photovoltaic Modules and Panels, UL See Glossary Section 2.17 for definition of Standard Test Conditions. 4 As an example, see NEC Sec where calculations for maximum circuit current and conductor ampacity involve multipliers of 125%. page 13

14 Fig. 8 Solar Irradiance for June 22, 2011 at Las Vegas Test Site Test Results Data measurements were recorded during the months of June, July and August of This time of the year also produced many days of large amounts of solar radiation for the longest periods of time. During these months there were many days of full sun throughout the day where outside temperature exceeded 100 o F, and solar irradiance exceeded 1000 W/m 2. The solar irradiance for days of prolonged full sun peaked near solar noon, which occurred at about 12:45 pm in Las Vegas that time of year (daylight savings time). For analysis of results purposes, 10 days were chosen during this time period where that solar irradiance exceeded 1000 W/m 2 for a prolonged period of time. Although wind speed could not be controlled, these days were also chosen where the wind speed was minimized. This resulted in 5 days in late June, and 5 days in early August as shown in Table 4. For each of these 10 days, the temperature data were analyzed for the period of time that day were the solar irradiance was greater than or equal to 1000 W/m 2. Depending upon the day, this resulted in elapsed times of 3 hours and 5 minutes to 2 hours and 15 minutes as shown in the table. This table also includes the average wind speed and maximum outdoor ambient temperature for that period of time. See Appendix C for complete graphs of the daily outdoor ambient temperature, solar irradiance, and wind speed. page 14

15 Table 4 10 Days of Analyzed Data Period of Solar Radiation 1000 W/m 2 (Hours:Minutes) Outdoor Avg Wind Speed Ambient Day (2011) Beginning End Elapsed Time (MPH) Deg F June 21 11:15 14:05 2 hr 50 min June 22 11:10 14:10 3 hr 00 min June 23 11:20 14:15 2 hr 55 min June 25 11:05 14:10 3 hr 05 min June 26 11:10 14:15 3 hr 05 min August 4 11:35 2 hr 25 min August 5 11:30 14:05 2 hr 35 min August 6 11:35 13:50 2 hr 15 min August 8 11:35 2 hr 25 min August 9 11:45 2 hr 15 min For each test sample, the rise above outdoor ambient temperature for the three thermocouple temperatures were averaged for each five-minute increment to record the temperature rise above outdoor ambient of the test sample for that time measurement increment. An analysis of the variance for the three thermocouple readings of each test sample typically showed a variance of less than 1 o F, except for the tray cable (TC) samples, where the variance was greater because of the orientation of the three thermocouples around the circumference of the cable. For that reason, the maximum temperature of the three thermocouple readings for the tray cable was used for this test sample because of the importance of recording the hottest temperature being experienced by the cable. For each of the ten chosen days, the maximum, minimum, 90 th, 75 th, and 50 th percentile temperatures were calculated for each test sample at each elevation for the period of time that day when the solar irradiance was greater than or equal to 1000 W/m 2. For the accumulated ten days, the overall maximum, minimum, and averages of the 90 th, 75 th and 50 th percentile temperatures were then tabulated. The tables below show that complied data. page 15

16 Table 5 Maximum Temperature Rise Above Outdoor Ambient ( o F) Distance Above Roof 1 Foot 3-1/2 inch 1/2 inch On Roof Circular Raceway - Metal 3/4" EMT /2" RMC /2" EMT /2" RMC " EMT " RMC Circular Raceway - Plastic 3/4" PVC /2" PVC " PVC Square Raceway - Metal 4" DUCT " DUCT Cables #12 MC #1/0 MC #1/0 SE Tray 1/0 SE Tray 1/0 TC #500 MC NEC Adder Table 6 Minimum Temperature Rise Above Outdoor Ambient ( o F) Distance Above Roof 1 Foot 3-1/2 inch 1/2 inch On Roof Circular Raceway - Metal 3/4" EMT /2" RMC /2" EMT /2" RMC " EMT " RMC Circular Raceway - Plastic 1/2" RMC /2" PVC " PVC Square Raceway - Metal 4" DUCT " DUCT Cables #12 MC #1/0 MC #1/0 SE Tray 1/0 SE Tray 1/0 TC #500 MC NEC Adder page 16

17 Circular Raceway - Metal Circular Raceway - Plastic Square Raceway - Metal Cables Table 7 90th Percentile Temperature Rise Above Outdoor Ambient ( o F) Distance Above Roof 1 Foot 3-1/2 inch 1/2 inch On Roof 3/4" EMT /2" RMC /2" EMT /2" RMC " EMT " RMC /4" PVC /2" PVC " PVC " DUCT " DUCT #12 MC #1/0 MC #1/0 SE Tray 1/0 SE Tray 1/0 TC #500 MC NEC Adder Table 8 75th Percentile Temperature Rise Above Outdoor Ambient ( o F) Distance Above Roof 1 Foot 3-1/2 inch 1/2 inch On Roof Circular Raceway - Metal 3/4" EMT /2" RMC /2" EMT /2" RMC " EMT " RMC Circular Raceway - Plastic 3/4" PVC /2" PVC " PVC Square Raceway - Metal 4" DUCT " DUCT Cables #12 MC #1/0 MC #1/0 SE Tray 1/0 SE Tray 1/0 TC #500 MC NEC Adder page 17

18 Table 9 50th Percentile Temperature Rise Above Outdoor Ambient ( o F) Distance Above Roof 1 Foot 3-1/2 inch 1/2 inch On Roof Circular Raceway - Metal 3/4" EMT /2" RMC /2" EMT /2" RMC " EMT " RMC Circular Raceway - Plastic 3/4" PVC /2" PVC " PVC Square Raceway - Metal 4" DUCT " DUCT Cables #12 MC #1/0 MC #1/0 SE Tray 1/0 SE Tray 1/0 TC #500 MC NEC Adder page 18

19 Data Analysis To analyze the differences between wiring systems at different distances from the roof, a compilation of all of the wiring system 90 th percentile temperature rises (Table 7) 5 for the period of time each day where the solar irradiance was greater than or equal to 1000 W/m 2 was made for each of the four elevations. This analysis is shown in Boxplot 6 No.1. Note that for the wiring systems at distances 0.0 and 0.5 inches above the roof, the roof color was black, and for distances 3.5 and 12.0 inches above the roof, the roof color was white. Previous research 7 had shown that at the 0.5 inch distance, there was no significant difference between the black and white roof colors affecting the temperature of the wiring systems. For that reason black was chosen for the color of the roof at that distance. However, this previous research was only conducted with smaller size raceways and cable. It is possible that larger size raceways and cables could have absorbed more of the reflected solar radiation off the roof had the roof been white. This could explain why the mean temperature rise for the wirings systems at 0.5 inches above the roof were less than those at 3.5 and 12.0 inches above the roof. To analyze the differences between the different individual wiring systems, a compilation of all of the different wiring system 90 th percentile temperature rises for the period of time each day where the solar irradiance was greater than or equal to 1000 W/m 2 was made. This analysis is shown in Boxplot No.2. Note that the MC and TC cables were black in color, and the SE cable was light gray in color. 5 The 90 th percentile values were used to eliminate the maximum temperatures that were only being experienced for a very short period of time when the solar irradiance peaked for that day. Note however, there was typically only a few degrees F or less difference between the 90 th and 75 th percentile values. See Tables 7 and 8. 6 See Appendix D for a description of boxplots. 7 Effect of Rooftop Exposure on Cable Temperatures, November 2008, by Travis C. Lindsey. Available for review at the National Fire Protection Association (NFPA) Headquarters, Quincy, MA. Reference Report on Proposals June 2010, Proposal 6-66, Log #2751, NEC-P06. See Fig. 3, Temperature Rise as Function of Roof Color. page 19

20 60 Boxplot No. 1 - All Temperature Data by Distance Above Roof Temperature Rise, Deg F Distance Above Roof (Inches) 12.0 page 20

21 Histogram No. 1 shows the 90 th percentile temperature rise data for wiring systems directly on the roof for the period of time each day where the solar irradiance was greater than or equal to 1000 W/m 2. This analysis shows that for all of the 17 test samples of wiring systems mounted directly on the roof, the mean (average) temperature rise was 48.8 o F with a standard deviation of 6.83 o F. Confidence intervals (C.I) are often used as a statistical estimate to bracket data parameters with a known degree of certainty. A 95% C.I. is suggested as an appropriate safety factor to represent the true population of the data from the sampled population (tested samples). A 95% C.I. is calculated (two-sided) as the mean plus/minus 1.96 times the standard deviation. For this case, maximum temperature rise for all wiring systems mounted directly on the roof with a 95% C.I. would be 62.2 o F. Histogram 1A shows a representation of this with vertical lines at the mean and 95% C.I. points. page 21

22 An observation from Boxplot No. 1 appears to show that there is little difference between mean temperature rises for test samples of wiring systems mounted 0.5, 3.5, and 12.0 inches above the roof. Neglecting any heat convection or reradiation from the surface of the roof, this would be expected since the distance from the sun to the surface of the earth is large as compared to the distance between the three wiring systems. To verify this, an analysis of variance (ANOVA) was conducted with this data for the three distances from the roof. This analysis, shown in Fig. 9, demonstrates there is little difference between the mean temperature rises for all test data from each of the three wiring systems mounted 0.5, 3.5, and 12.0 inches above the roof. This is exemplified by the low value for R sq, which shows that varying the distance from the roof between 0.5 and 12.0 inches does not have any significant effect on the temperature rise within the raceway or cable. It is expected that distances greater than 12.0 inches will also show this minimal difference. page 22

23 One-way ANOVA: 90 th Percentile Data versus Distance from Roof (0.5, 3.5, and 12.0 inches) Source DF SS MS F P Distance Error Total S = 6.6 R-Sq = 6.31% R-Sq(adj) = 2.41% DF = Degrees of Freedom SS = Sum of squares MS = Mean square S = Standard deviation F = F ratio P = p-value R = Correlation coefficient Individual 95% C.I.s for Mean Based on Pooled Standard Deviation of 6.6 Level N Mean StDev ( * ) ( * ) ( * ) Fig. 9 Analysis of Variance for Wiring Systems Mounted Off Roof Histogram No. 2 shows the 90 th percentile temperature rise data for all wiring systems mounted 0.5, 3.5, and 12.0 inches above the roof for the period of time each day where the solar irradiance was greater than or equal to 1000 W/m 2. page 23

24 This analysis shows that for all of the 51 test samples of wiring systems mounted off the roof (0.5, 3.5, and 12.0 inches), the mean temperature rise was 38.5 o F with a standard deviation of 6.60 o F. The maximum temperature rise for all wiring systems mounted off on the roof with a 95% C.I. would be 51.4 o F. Histogram 2A shows a representation of this with vertical lines at the mean and 95% C.I. points. page 24

25 SUMMARY 1. Of the 17 different wiring systems tested, nine are currently addressed by the 2011 NEC Sec (B)(3)(c) requirement for circular raceways exposed to sunlight on rooftops, e.g., EMT, RMC, and PVC, and eight are not, e.g., square raceway and cables. Using the maximum temperature rises from Table 5: a. All of the wiring systems mounted 12 inches from the roof and 3-1/2 inches from the roof exceeded the NEC Table 310.(B)(3)(c) temperature adders of 25 o F and 30 o F respectively. For wiring systems mounted 12 inches from the roof, this ranged from 34.2 to 59.6 o F, and for wiring systems 3-1/2 inches from the roof this ranged from 35.1 to 65.0 o F. b. For wiring systems mounted ½ inch off the roof, all of the cables, and the 4 inch square metal duct exceeded the 40 o F NEC temperature adder. Five of the nine circular raceways also exceeded this 40 o F adder. The range in temperature rises for wiring systems mounted ½ inch off the roof was 34.8 to 53.3 o F. c. For wiring systems mounted on the roof, four of the cables exceeded the 60 o F temperature adder, and three of the circular raceways also exceeded this 60 o F adder. The range in temperature rises for wiring systems mounted on the roof was 43.8 to 71.4 o F. 2. In general, the smaller size wiring systems reached a hotter temperature than wiring systems of the same type but larger. This was especially true of the metallic wiring systems, and when the wiring systems were mounted directly on the roof. This was expected because the larger wiring systems had a larger ratio of surface area to mass, and thus took longer to heat up and cool down. This greater mass could also absorb the radiated heat from the sun (and the conducted heat from the roof) over a greater volume. See Tables The 1/0 SE cable operated much cooler than the similar sized 1/0 MC and 1/0 TC cables. This was expected due to the black outer jacked of the 1/0 MC and 1/0 TC cables having greater absorption properties, e.g., higher emissivity, than the lighter colored SE cable. See Boxplot No. 2. page 25

26 4. Wiring systems mounted 3-1/2 inches off the white roof usually operated hotter than similar wiring systems mounted ½ inch off the black roof. This was likely because of the solar reflection off the white roof producing additional solar power that could be absorbed by the underside of the wiring system 3-1/3 inches from the roof. These results may have been different had the wiring systems mounted ½ inch off the roof been tested with a white roof. However, wiring systems mounted directly on the roof most always operated significantly hotter than wiring systems of the same type mounted off the roof. See Boxplot No For all wiring systems mounted directly on the roof, the 90 th percentile mean temperature rise above outdoor ambient for the period of time each day where the solar irradiance was greater than or equal to 1000 W/m 2 was 48.8 o F with a standard deviation 6.8. For this case, maximum temperature rise above outdoor ambient for all wiring systems mounted directly on the roof with a 95% confidence interval (C.I.) would be 62.2 o F. 6. A statistical analysis of variance of the data for temperature rise above outdoor ambient showed that all test data from wiring systems mounted 0.5, 3.5, and 12.0 inches above the roof were not affected significantly by distance. Therefore, distances greater than 0.5 inches above the roof can be considered far from the roof and roof distance does not need to be a consideration in calculating temperature rise. For all wiring systems mounted 0.5, 3.5, and 12.0 inches above the roof, the 90 th percentile mean temperature rise above outdoor ambient for the period of time each day where the solar irradiance was greater than or equal to 1000 W/m 2 was 38.5 o F with a standard deviation 6.6. For this case, maximum temperature rise above outdoor ambient for all wiring systems mounted off on the roof with a 95% confidence interval (C.I.) would statistically be 51.4 o F. Report by: Reviewed by: David A. Dini, P.E. Research Engineer I Corporate Research Underwriters Laboratories Inc. Paul W. Brazis Jr., PhD Research Manager Corporate Research Underwriters Laboratories Inc. page 26

27 APPENDIX A Test Samples 1. Metal-Clad Cable, Type MC, No. 12 AWG/3 with No. 12 AWG ground. Aluminum interlocked armor with black PVC jacket. Copper THHN/THWN conductors. 2. Rigid Metal Conduit, Type RMC, Trade Size ½. Metallic silver in color. Seven No. 12 AWG copper conductors, Type THHN/THWN installed. 3. Rigid Polyvinyl Chloride Conduit, Type PVC, Trade ¾. Natural gray in color. Three No. 12 AWG copper conductors, Type THHN/THWN installed. Fig. A1 No. 12 MC (1), ½ RMC (2), ¾ PVC (3) 4. Electrical Metallic Tubing, Type EMT, Trade Size ¾. Metallic silver in color. Three No. 12 AWG copper conductors, Type THHN/THWN installed. 5. Metal-Clad Cable, Type MC, No. 1/0 AWG/3 with No. 6 AWG ground. Aluminum interlocked armor with black PVC jacket. Copper THHN/THWN conductors. page 27

28 6. Service-Entrance Cable, Type SE, No. 1/0 AWG/3 with No. 2 AWG ground. Sunlight resistant with light gray jacket. Copper THHN/THWN conductors. 7. Rigid Metal Conduit, Type RMC, Trade Size 1-½. Metallic silver in color. Four No. 1/0 AWG copper conductors, Type THHN/THWN installed. Fig. A2 ¾ EMT (4), No. 1/0 MC (5), No. 1/0 SE (6), 1-1/2 RMC (7) 8. Rigid Polyvinyl Chloride Conduit, Type PVC, Trade1-1/2. Natural gray in color. Three No. 1/0 AWG copper conductors, Type THHN/THWN installed. 9. Electrical Metallic Tubing, Type EMT, Trade Size 1-1/2. Metallic silver in color. Five No. 1/0 AWG copper conductors, Type THHN/THWN installed. page 28

29 Fig. A3 1-1/2 PVC (8), 1-1/2 EMT (9) 10. Service-Entrance Cable, Type SE, No. 1/0 AWG/3 with No. 2 AWG ground. Sunlight resistant with light gray jacket. Copper THHN/THWN conductors. Installed in a cable tray, basket type. 11. Power and Control Tray Cable, Type TC, No. 1/0 AWG/3 with No. 6 AWG bare ground. Sunlight resistant with black jacket. Copper THHN/THWN conductors. Installed in a cable tray, basket type. Fig. A4 No. 1/0 SE (10), No. 1/0 TC (11), Installed in Cable Tray page 29

30 12. Metal-Clad Cable, Type MC, No. 500 kcmil/3 with No. 2 AWG ground. Aluminum interlocked armor with black PVC jacket. Copper THHN/THWN conductors. 13. Rigid Metal Conduit, Type RMC, Trade Size 4. Metallic silver in color. Three No. 500 kcmil copper conductors, Type THHN/THWN installed. Fig. A5 No. 500 MC (12), 4 RMC (13) 14. Rigid Polyvinyl Chloride Conduit, Type PVC, 4. Natural gray in color. Three No. 500 kcmil copper conductors, Type THHN/THWN installed. 15. Electrical Metallic Tubing, Type EMT, Trade Size 4. Metallic silver in color. Three No. 500 kcmil copper conductors, Type THHN/THWN installed. page 30

31 Fig. A6 4 PVC (14), 4 EMT (15) 16. Metal Wireway, 4 in. by 4 in., 16 gauge steel. Gray in color. Three No. 1/0 AWG copper conductors, Type THHN/THWN installed. 17. Metal Wireway, 8 in. by 8 in., 14 gauge steel. Gray in color. Three No. 500 kcmil copper conductors, Type THHN/THWN installed. Fig. A7 4 In. Duct (16), 8 In. Duct (17) page 31

32 APPENDIX B Test Instrumentation Pyranometer Campbell Scientific, CS300 apogee silicon pyranometer. Anemometer - Campbell Scientific, three-cup anemometer. Data Acquisition System - Campbell Scientific, CR5000 Measurement and Control System. Serial No Date of last calibration, April 15, 2011, by Campbell Scientific (A2LA accredited). page 32

33 APPENDIX C Graphs of Daily Outdoor Ambient Temperature, Solar Irradiance, and Wind Speed page 33

34 June 21, Ambient Temperature Deg F June 21, Solar Watts / square meter June 21, Wind Velocity MPH page 34

35 112 June 22, 2011 Ambient Temperature Deg F June 22, 2011 Solar Watts / square meter June 22, Wind Velocity MPH page 35

36 110 June 23, 2011 Ambient Temperature Deg F June 23, 2011 Solar Watts / square meter June 23, Wind Velocity MPH page 36

37 106 June 25, Ambient Temperature Deg F June 25, 2011 Solar Watts / square meter June 25, Wind Velocity MPH page 37

38 107.5 June 26, 2011 Ambient Temperature Deg F June 26, 2011 Solar Watts / square meter June 26, Wind Velocity MPH page 38

39 106 August 4, 2011 Ambient Temperature Deg F August 4, Solar Watts / square meter August 4, Wind Velocity MPH page 39

40 105.0 August 5, 2011 Ambient Temperature Deg F August 5, Solar Watts / square meter August 5, Wind Velocity MPH page 40

41 106 August 6, 2011 Ambient Temperature Deg F August 6, Solar Watts / square meter August 6, Wind Velocity MPH page 41

42 107.5 August 8, 2011 Ambient Temperature Deg F August 8, Solar Watts / square meter August 8, Wind Velocity MPH page 42

43 107.5 August 9, 2011 Ambient Temperature Deg F August 9, Solar Watts / square meter August 9, Wind Velocity MPH page 43

44 APPENDIX D Description of Boxplot Diagrams for Data Analysis Note A crosshairs within a box also represents the mean (average) of the data. page 44